The invention relates generally to apparatus for high energy imaging and other radiation imaging systems, and more particularly, a collimator apparatus and fabrication process.
Radiation imaging systems are widely used for medical and industrial purposes, such as for x-ray computed tomography (CT) for example. In a CT system, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane of a Cartesian coordinate system, termed the “imaging plane.” The x-ray beam then passes through the object being imaged, such as a medical patient, and impinges upon a multi-row multi-column detector array.
Some CT systems utilize CT detectors with collimators fabricated from individual high density, high atomic number plates, like tungsten plates, and high density, high atomic wires at ninety degree angles to the plates. The plates function to eliminate scattered x-rays that compromise CT image quality.
Tungsten plates in the collimator assembly have dimensions of up to 200 microns in width. This width represents more material than is required for just the collimation of scattered x-rays. The width dimension is needed however, for the collimator's second function, the shielding of the scintillator edges, shielding of the reflector material and shielding of the photodiode. The collimator assembly is also designed with a high aspect ratio, height (or overall thickness in the y-direction) to length (or overall spacing in the X-direction), for the efficient collimation of scattered radiation. This aspect ratio results in a larger depth (in the y-direction) for x-ray penetration shielding than is required.
CT detectors also use reflectors that are composed of organic reflector composites which are formed in gaps between the scintillators. Reflectors are composed of organic reflector composites or are made of layers, where one layer is lead or some other highly x-ray absorbing material. These reflectors do, at best, a modest job in attenuating scattered x-rays. Composite structures of the reflectors present challenges in manufacturing and lending themselves to small cells with small gaps. Alternatives to these constructions have been found in high x-ray attenuating pigments in organic reflector composites, but these present their own challenges in attenuating scattered x-rays. These challenges arise from the maximum amount of attenuating pigment that can be loaded into into the organic reflector composite and the impact on overall reflector reflectivity.
Accordingly, there is a need for a collimator assembly that provides improved manufacturability and costs, and allows separation of the collimator functions into scatter collimation and x-ray shielding, which in turn, allows individual optimization of each function, improving overall detector performance.